打字稿类型'数字'不可分配│键入'字符串' [英] Typescript Type 'number' is not assignable │ to type 'string'

问题描述

我目前正在为Angular 4应用制定货币格式指令.在解析后，除去数字和小数点以外的所有内容，最后得到一个字符串化的浮点数，但是我需要它以浮点数形式返回，以便我可以对其进行数学运算.

I am currently knee deep in making a currency formatter directive for an Angular 4 app. on the parse strip out everything other than the numbers and the decimal and end up with a stringified float, but I need it to return as a float so I can do math with it.

parse(value: string, fractionSize: number = 2): number {
  let val = value.replace(/([^0-9.])+/ig, '');
  let [ integer, fraction = "" ] = (val || "").split(this.DECIMAL_SEPARATOR);
  integer = integer.replace(new RegExp(this.THOUSANDS_SEPARATOR, "g"), "");
  fraction = parseInt(fraction, 10) > 0 && fractionSize > 0
    ? this.DECIMAL_SEPARATOR + (fraction + PADDING).substring(0, fractionSize)
    : "";
  let result = `${integer}${fraction}`;
  // at this point result = "100.55";
  result = parseFloat(result); // this refuses to compile saying "Type 'number' is not assignable │ to type 'string'"
  return result;
}

推荐答案

两行:

let result = `${integer}${fraction}`;
result = parseFloat(result);

是问题所在.当未明确声明变量时，Typescript可以很好地推断出变量的类型.在这种情况下，由于您将字符串分配给 result ，因此typescript推断其类型为字符串.要解决此问题，您有两个选择.首先，显式声明该变量的类型，以便它允许包含字符串和数字:

are the problem. Typescript is pretty good about infering the type of a variable when it's not explicitly declared. In this case, because you assign a string to the result, typescript infers it's type as a string. To fix this, you have two options. First, explicitly declare the type of that variable so that it allows both strings and numbers:

let result: string|number = `${integer}${fraction}`;
result = parseFloat(result); // now should be ok.

或者您可以将解析后的数字分配给新变量，而不是重新使用 result 变量:

Or you can assign the parsed number to a new variable, instead of reusing the result variable:

let result = `${integer}${fraction}`;
let numberResult = parseFloat(result); // now should be ok.

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